Method for producing metal shapes with a polygonal cross-section by means of continuous casting on a double-flanged wheel and continuous rolling

ABSTRACT

The invention relates to a method for producing metal shapes with a partially or totally polygonal cross-section by means of continuous casting in a double-flanged wheel and continuous rolling using a series of at least 3 pairs of rollers with a peripheral flange, whereby said rollers are alternately horizontally and vertically disposed in a symmetrical position with respect to said shape. The inventive method is characterised in that the flanges of the first pairs of rollers are identical to those used to produce shapes with a circular cross-section; the last pair of rollers has flanges defining a section that corresponds substantially to that of the desired shape; the section formed by the grooves of the last pair of rollers has curve radiuses of between 1 and 5 mm at the highest points of the polygon; the sides of the polygon that are not parallel to the air gap pertaining to the last pair of rollers have a clearance angle of ½-3° in comparison with the corresponding of the section of the final shape. The invention can be used to produce copper or aluminum alloy shapes for drawing or and/or subsequent redrawing.

FIELD OF THE INVENTION

The invention concerns a process for manufacturing metal sections, inparticular in aluminium alloys, continuously rolled by a series of pairsof rollers from an as-cast bar obtained by continuous casting in agrooved wheel, possibly followed by one or more stages of discontinuousor continuous wire drawing and annealing.

DESCRIPTION OF THE RELATED ART

For many years wire rod has been manufactured in non-ferrous alloys,particularly in aluminium alloys, from an as-cast bar continuously castin the groove of a wheel which is rotated, the groove being blanked offby a tape engaged by the wheel. Known casting systems are those with 2wheels with a small support wheel, 3 wheel systems, like the Properzicasting described in GB patent 1143264, 4 wheel systems like thePechiney 4R casting described in FR 1178580, and 5 wheel systems likethe one described in US 3416596.

The as-cast bar, of generally triangular or trapezoidal cross-section,is then continuously rolled through a series of successive stands madeup of two rollers, and alternately horizontal and vertical, so as toobtain a wire of circular cross-section, which may be used as such ortransformed by drawing.

In the case of aluminium alloys the process is widely used for lightalloys, intended particularly for electrical conductors. With someadaptations, described for example in the patents FR 2234936 (Secim andPechiney Aluminium), FR 2304414 (Secim) and FR 2359613 (PechineyAluminium), it has been possible to cast and roll without causingporosities of more heavily alloyed alloys with a higher solidificationrange, such as alloys of the 2000, 5000 and 7000 series according to thedesignations of the Aluminum Association, which can be used formechanical applications.

To the knowledge of the applicant company, none of the existingcontinuous casting-roll machines has ever manufactured products of noncircular cross-section. To be sure, it is normal to use round wire rodwhen the drawn end product is itself a round wire, which is the case forexample for electrical conductors or wire for netting. There are,however, particularly in mechanical applications, drawn products of noncircular cross-section, for example rectangular, triangular, polygonalor T-shaped, for which it would be more economical to start from a wirerod of related shape, which would reduce drawing passes, or even toleave the casting-roll machine in the final size without subsequentdrawing.

One of the reasons which might explain the absence on the market of wirerod of non circular cross-section stems from the difficulty ofcontrolling the geometry of the section during rolling. For a circularcross-section in fact, the product emerging from the final rolling standremains on the groove of the rollers only via a generator, and itsseparation at output poses no problem. It is not the same for productswhose cross-section comprises a plane part, for example a rectangular,triangular or T-shaped cross-section. They remain on the groove of therollers of the final stand in a more or less wide band, the unevendetachment of which entails distortions in the geometry of the rolledproduct, as well as surface defects.

SUMMARY OF THE INVENTION

The purpose of the invention is to overcome this drawback and to allowaccurate control of the geometry of the cross-section of the rolledproduct, when this cross-section comprises a polygonal part, i.e. atleast two straight secant parts. The rolled section can then be useddirectly as it is, either continuously or discontinuously drawn so as toobtain a wire of non circular cross-section, with a smaller number ofpasses than starting with a circular section.

An object of the invention is a process for manufacturing metal sectionsof partially or totally polygonal cross-section by continuous casting ina grooved wheel and continuous rolling by means of at least 3 andpreferably 3 to 8 pairs of rollers fitted with a peripheral groove,these rollers being placed symmetrically relative to the section, andalternately horizontal and vertical, a process which is characterised inthat:

the grooves of the first pairs of rollers are identical to those of therollers used for the manufacture of sections of circular cross-section,

the final pair of rollers comprises grooves delimiting a cross-sectionapproximately corresponding to that of the section desired,

the cross-section formed by the grooves of the final pair of rollers hasat the apexes of the polygon radii of curvature between 1 and 5 mm,

the sides of the polygon non parallel to the gap of the final pair ofrollers have, relative to the corresponding sides of the cross-sectionof the final section a clearance between ½ and 3°.

An object of the invention is also a process for manufacturingdiscontinuously or continuously drawn metal sections of partially ortotally polygonal cross-section from as-cast bars of partially ortotally polygonal cross-section obtained by continuous casting in agrooved wheel and continuous rolling, in which the number ofdiscontinuous or continuous wire drawing passes and the number ofannealings are each reduced by at least one third relative to theprocess of the prior art starting from an as-cast bar of approximatelycircular cross-section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a machine for continuous casting on a grooved wheel and thebattery for continuous rolling of the as-cast bar.

FIGS. 2 to 5 show, in cross-section along the plane of their axes ofrotation, the final pair of rollers used for the rolling of the sectionsdescribed in examples 1 to 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The manufacturing process according to the invention uses a castingmachine comprising a liquid metal feed nozzle (1), a casting wheel (2),which is rotated, fitted with a peripheral groove, blanked off by ametal tape (3) engaged by the wheel. The machine may be a two-wheelmachine and a follower wheel like the one shown in FIG. 1, the secondwheel (4) serving to tension the tape, and the follower wheel (5) beingintended to keep the tape on the casting wheel in the vicinity of thecasting area. The machine may also be a three, four or five wheelmachine. The cross-section of the as-cast bar (6), generally trapezoidalin shape, varies according to the installations between 900 and morethan 3000 mm².

The number of rolling stands (7), each comprising a pair of rollers, isgreater than two and preferably between 3 and 8. This number depends onthe final cross-section to be obtained, since the initial cross-sectionis connected to the casting machine and cannot therefore be modifiedeasily. The reduction of cross-section in each stand is, generally,between 10 and 40%. The accuracy of the geometry improves with thenumber of stands, but inversely a high number of stands tends to workharden the metal, which makes subsequent drawing more difficult. Thefirst stands use rollers with the same grooves as those used for rollingwire of circular cross-section. The penultimate stand may comprise, ascircumstances require, rollers identical to the first, either flatrollers, or rollers close in shape to the rollers of the final stand,which rollers have in all cases grooves delimiting a cross-sectioncorresponding to the final cross-section desired.

However, experience has shown that if this cross-section is too close tothe final cross-section, acceptable dimensional tolerances cannot beobserved. Likewise, experience has shown that if the radii of curvaturebetween the plane faces are too small, the metal tends to adhere to therollers, which causes incidents on the line and imposes stoppages.According to the invention, these drawbacks are avoided by adapting theshape of the groove of the finisher rollers, which provides easywithdrawal and good filling of the shapes of the grooves. Thisadaptation is obtained by providing radii of curvature between the planefaces between 1 and 5 mm, and, for the faces not parallel to the gap ofthe rollers, clearances, i.e. angles between the groove and thecorresponding face of the section, between ½ and 3°.

Special precautions must be taken in winding the section at the end ofrolling. Unlike when winding wire of circular cross-section, a smallspace must be provided between the coils and they must not be allowed tooverlap.

The continuous casting process according to the invention allows metalsections to be made, particularly in aluminium alloys or copper, ofsquare, rectangular, triangular and more generally partially or totallypolygonal cross-section, with good dimensional tolerances, of about 0.1mm, and with good detachment of the metal from the last rolling stand.

These sections may be used as such in numerous mechanical or electricalapplications, or for the manufacture of weld wire. They can also betransformed by discontinuous or continuous wire drawing in one or morepasses, in order to confer on them dimensions, tolerances on dimensionsand shape, or particular mechanical characteristics. Some of theseproducts, obtained from wire rod of circular cross-section, are known.The fact of using as an as-cast bar for continuous or discontinuous wiredrawing a wire rod of partially or totally polygonal cross-sectionaccording to the invention considerably Simplifies the manufacturingprocess since the shape of the transverse cross-section of the as-castbar can be very close to that of the drawn product required.Furthermore, leaks of lubricant between the metal and the die obtainedwhen the geometry of the as-cast bar and that of the die are toodifferent are avoided. The manufacturing process for discontinuously orcontinuously drawn wire of partially or totally polygonal cross-sectionaccording to the invention is characterised in that a selection is made,for a given cross-section of the final section, of a cross-section ofthe as-cast bar such that the number of discontinuous or continuous wiredrawing passes and annealings can be minimised. Relative to a wire rodof approximately circular cross-section, and by choosing for eachdiscontinuous or continuous wire drawing pass, a work hardening rate E(input cross-section—output cross-section)/output cross-section close tothe maximum value (about 80% for aluminium alloys) that the wire canwithstand without developing crippling defects, the professional is ableto define, for a wire in an aluminium or copper alloy, a range ofmanufacture such that the number of discontinuous or continuous wiredrawing passes and the number of annealings are each reduced by at leastone third. This gain is greater for cross-sections which, at leastlocally, are the furthest removed from a circular cross-section (V or Tcross-sections, very elongated flats and particularly those having across-section such that the ratio of width to thickness is greater than2).

The exact number of discontinuous or continuous wire drawing passesdepends on the type of alloy used, as well as on the parameters of thediscontinuous or continuous wire drawing process. For aluminium alloysand sections of square or triangular cross-section, discontinuous orcontinuous wire drawing can most often be limited to a single pass withone annealing, instead of at least two passes and two annealingsstarting from a circular as-cast bar. For sections of rectangularcross-section with a ratio of width to thickness between 1 and 2,discontinuous or continuous wire drawing can be limited to two passesand one annealing, and for width to thickness ratios between 2 and 5, tothree passes and two annealings. Sections of rectangular cross-sectionwith a width to thickness ratio greater than 4 are moreover verydifficult to make by drawing from an as-cast bar of round cross-section,with the result that the process according to the invention allows anenlargement of the possibilities of manufacture of wire works.

The process according to the invention can be used for a great varietyof metal alloys, particularly aluminium alloys, including heat treatablealloys (2000, 6000 and 7000 series) and cuprous alloys.

EXAMPLES

For all the examples, the metal was cast on a continuous casting machineof the 3 wheel type, in a grooved wheel leading to an as-cast bartrapezoidal in shape, of greater width 41 mm and of a height of 29 mm,i.e. an as-cast bar cross-section of 1050 mm².

Example 1

From an as-cast bar of 1050 mm² cross-section, in aluminium alloy 5754according to the designation of the Aluminum Association, a section ismade of square cross-section 13×13 mm, by rolling through 6 stands, eachcomprising a pair of rollers circular in shape made of Z38CDV5 steelprocessed at 52 HRC. On leaving each stand the speeds are obtained thatare mentioned in table 1, as well as the cross-sections falling withinthe formats shown in the same table:

TABLE 1 cross-section Stand no. of rollers format (mm × mm) speed (m/s)1 Standard 45 × 19.5 19 2 Standard 27 × 26 29.5 3 Standard 33 × 13.9 384 Standard 17.5 × 18 57 5 Flat clearance 12.5 83 6 Square 13.2 × 13.2 84

The first 4 pairs of rollers have grooves delimiting a circularcross-section, as is the case for the continuous rolling of sections ofcircular cross-section. The fifth pair of rollers delimits a flat gapand the sixth delimits a square cross-section very close to that of thefinished product. The gap between the rollers of this sixth pair is 2mm. The radii of curvature of the cross-section of the grooves of therollers at the 4 apexes of the square are 3 mm. The clearances on theperpendicular square sides at the gap of the rollers are of 1°.

No adhesion of the section on the output rollers is obtained and thetolerances on the cross-section of the section are less than 0.1 mm.

Example 2

Starting from an as-cast bar of the same cross-section as in theprevious example, a flat is made of rectangular cross-section 16.5×8.1mm of aluminium alloy 2017, by continuous rolling through 6 stands. Thetypes of rollers used, the formats and the speeds on leaving each standare given in table 2.

TABLE 2 cross-section Stand no. of rollers format (mm × mm) speed (m/s)1 standard 45 × 19.5 19 2 standard 27 × 26 29.5 3 standard 33 × 13.9 384 standard 17.5 × 18 57 5 standard 21.6 × 10.2 83 6 rectangular 16.5 ×8.1 114

The first 5 Pairs of rollers have standard grooves similar to those usedfor the rolling of sections of circular cross-section. The sixth pairhas a gap of 1.5 mm and its grooves delimit a rectangle the apexes ofwhich have a radius of curvature of 2 mm and the sides perpendicular tothe gap a clearance of 1°. No adhesion of the section on leaving thelast stand is noted and the tolerances on the dimensions of the sectionare less than 0.1 mm.

Example 3

A section is made of aluminium alloy 1370 having a cross-section in thegeneral shape of a circular sector, delimited by a triangle below and acircle arc above, falling within a rectangle 16.2×12.2 mm, and ofcross-section 150 mm². The types of rollers, the formats and the speedson leaving each stand are shown in table 3

TABLE 3 cross-section Stand no. of rollers format (mm × mm) speed (m/s)1 standard 45 × 19.5 19.6 2 standard 27 × 26 30.1 3 standard 33 × 14.641.2 4 standard 18 × 18 64.2 5 sector 17.3 × 14.8 88.2 6 sector 12.2 ×16.2 114

The first 4 pairs of rollers have standard grooves similar to those ofthe rollers used for the continuous rolling of the sections of circularcross-section. The grooves of the fifth pair delimit a cross-section inthe shape of a sector. The sixth pair has grooves delimiting across-section in the shape of a circular sector, with a radius ofcurvature of 3 mm between the 2 plane parts, a clearance of 1° on theseplane parts and a gap between the 2 rollers of 1.5 mm. The upper part ofthe cross-section, in the shape of a circle arc is carefully polished.No adhesion of the section on leaving the last stand is noted and thetolerances on the dimensions of the section are less than 0.1 mm.

Example 4

A section is made, intended for electrical applications, of aluminiumalloy 1370 in the shape shown in FIG. 4 of cross-section 490 mm². Thetypes of rollers, the formats and the speeds on leaving each stand areshown in table 4.

TABLE 4 cross-section Stand no. of rollers format (mm × mm) speed (m/s)1 standard 45 × 20.5 18 2 flat 28 × 19.5 28 3 shaped 32

Only 3 stands are used, only the first of which has standard rollers.The second stand has flat rollers and the third has rollers the groovesof which delimit the cross-section desired. For this final pair, theradii of curvature at the apexes of the sharp angles are 1.1 mm and theclearances on the vertical faces of 1.5°. The grooves are very carefullypolished. The gap used is 2 mm.

Example 5

A square wire is made of square cross-section 10 mm×10 mm of aluminiumalloy 5754, intended for the manufacture of bolts for fixing bakelitehandles onto culinary utensils made of aluminium, by drawing in a singlepass starting from the section of square cross-section 13×13 mmdescribed in example 1. The usual range according to the prior artstarted from an as-cast bar of circular cross-section of 18 mm diameterand comprised two drawing passes, separated by an annealing-greasing in13×13 mm format.

Example 6

A flat wire is made of cross-section 15.0×4.0 mm of aluminium alloy 2017starting from a flat section of rectangular cross-section 16.5×8.1 mmdescribed in example 2, by drawing into one three drawing passes,separated by an annealing-greasing in the intermediate formats 16.0×6.3mm and 15.65×4.45 mm. The usual range according to the prior art startedfrom an as-cast bar of circular cross-section of 18 mm diameter andcomprised 6 passes of drawing separated each time by anannealing-greasing in the intermediate formats 17.3×13.8 mm, 16.6×10.7mm, 16.2×8.2 mm, 16.0×16.3 mm, 15.65×4.85 mm.

What is claimed is:
 1. A process for manufacturing a metal profile ofpartially or totally polygonal cross-section comprising the steps ofcontinuously casting metal in a grooved wheel and continuously rollingthe cast metal by means of at least 3 pairs of rollers fitted with aperipheral groove, said rollers being placed symmetrically relative tothe profile, and alternately horizontal and vertical, wherein: therollers are arranged such that the grooves of the first pairs of rollersare identical to the grooves of the rollers used for the manufacture ofprofiles of circular cross-section, the rollers are arranged such thatthe final pair of rollers comprises grooves delimiting a cross-sectionapproximately corresponding to that of a desired profile, thecross-section formed by the grooves of the final pair of rollers has atapexes of a polygon, radii of curvature between 1 and 5 mm, and thesides of the polygon non parallel to the gap of the final pair ofrollers have, relative to corresponding sides of the cross-section ofthe final profile, a clearance angle between ½ and 3°.
 2. A processaccording to claim 1, wherein the profile has a square or rectangularcross-section.
 3. A process according to claim 2, wherein the profilehas a rectangular cross-section with a width/thickness ratio >4.
 4. Aprocess according to claim 3, wherein the profile has a triangularcross-section.
 5. A process according to claim 1, wherein the profilehas a T-shaped or V-shaped cross-section.
 6. A process according toclaim 1, additionally comprising a pair of rollers having a planesurface in a penultimate position.
 7. A process according to claim 1,followed by at least one discontinuous or continuous wire drawing passstep and optionally by at least one annealing step.
 8. A processaccording to claim 7, wherein the number of drawing pass steps and thenumber of annealing steps are each reduced by at least one thirdrelative to a process which would use as an as-cast bar fordiscontinuous or continuous wire drawing a wire rod of approximatelycircular cross-section to obtain a similar product.
 9. A processaccording to claim 8, wherein the profile is made of an aluminum alloy,of square or triangular cross-section and the process includes only onediscontinuous or continuous wire drawing pass and only one annealingstep.
 10. A process according to claim 9, wherein the aluminum alloy isa 5000 series alloy.
 11. A process according to claim 10, wherein thealuminum alloy is a 5756 alloy.
 12. A process according to claim 8,wherein the profile is made of an aluminum alloy of rectangularcross-section with a width to thickness ratio between 2 and 5, and thatthe process includes at least 3 discontinuous or continuous wire drawingpass steps and 2 annealing steps.
 13. A process according to claim 12,wherein the aluminum alloy is a 2000 series alloy.
 14. A processaccording to claim 13, wherein the aluminum alloy is a 2017 alloy.
 15. Aprocess according to claim 8, wherein the profile is made of an aluminumalloy of rectangular cross-section with a width to thickness ratiobetween 1 and 2, and the process includes at least 2 discontinuous or 3continuous wire drawing pass steps and one annealing step.
 16. A processaccording to claim 1, wherein there are from 3 to 8 pairs of rollers.